
class Node {
    constructor(val) {
        this.val = val;  
        this.next = null;  
    }
    //查  
    find(val) {
        var cur = this.head;

        while (cur.val.next === null) {
           if (cur == this.head) {
                return null;
            } 
            if(cur.val == val){
                return cur;
            }
            cur = cur.next;
        }
        
    }
    //增
    add(val) {
        var news = new Node(val);
        var cur = this.Last();   
        news.next = cur.next;
        cur.next = news;
    }
    
    //删
    remove(item) {
        const cur = new ListNode(0, head);
        if (cur.val === item) {
            cur.next = cur.next.next;
        }
        if (cur.next === this.head) {   
            return null;
        }
    }
    // 改
    change(val,news) {
        if (node.val = val) {
            node.val = news;
        }
    }
}